Spin Valve Transistor

Evolution Of Spintronics

        Spintronics came into light by the advent of Giant Magneto Resistance (GMR) in 1988. GMR is 200 times stronger than ordinary Magneto Resistance.  It results from subtle electron – spin effects in ultra multilayers of magnetic materials that cause a huge change in electrical resistance.

A spin valve multilayer serves as a base region of an n silicon metal base transistor structure.  Metal base transistors have been proposed for ultrahigh frequency operations because of 1.  Negligible base transport time. 2. Low base resistance, but low gain prospects have limited their emergence.  The first evidence of a spin valve effect for hot electrons in Co/Cu multilayers is the spin valve transistor. In this we see a very large change in collector current (215% at 77K) under application of magnetic field of 500 Oe.

Abstract

        In a world of ubiquitous presence of electrons can you imagine any other field displacing it? It may seem peculiar, even absurd, but with the advent of spintronics it is turning into reality. In our conventional electronic devices we use semi conducting materials for logical operation and magnetic materials for storage, but spintronics uses magnetic materials for both purposes. These spintronic devices are more versatile and faster than the present one. One such device is spin valve transistor.

Temperature Effects

        Transport property of hot electron is not fully understood at very low energy regime at finite temperatures. So, It is necessary to probe the temperature dependence of the hot electron transport property in relation to the SVT. The collector current across the spin valve changes its relative orientation of magnetic movements at finite temperature. Surprisingly the collector current showed different behaviors depending on the relative spin orientation in Ferro Magnetic layers. The parallel collector current is increasing up to 200 K and decreasing after that, while anti-parallel collector current is increasing up to room temperature. Actually in ordinary metals, the scattering strength increases with temperature T.

Introduction

        Two experiments in 1920’s suggested spin as an additional property of the electron.  One was the closely spaced splitting of Hydrogen spectralines, called fine structure.  The other was Stern –Gerlach experiment, which in 1922 that a beam of silver atoms directed through an inhomogeneous magnetic field would be forced in to two beams.  These pointed towards magnetism associated with the electrons.

         Spin is the root cause of magnetism that makes an electron tiny magnet.  Magnetism is already been exploited in recording devices. 

Conclusion

Now it is clear that, Spinvalve transistor is more versatile and more robust but it needs further fabrication methods to improve magnetic sensitivity of collector current. The greatest hurdle for spintronic engineers may be controlling all that spin. To do it on a single transistor is already feasible while to do it on a whole circuit will require some clever ideas.